President Barack Obama signs the "Every Student Succeeds Act," a major education law setting U.S. public schools on a new course of accountability, Thursday, December 10, 2015, in Washington.

The sweeping new federal education law known as the Every Student Succeeds Act (ESSA) has drawn praise from educators and lawmakers who had become increasingly frustrated with No Child Left Behind, the controversial federal education law on the books since 2002.

But one group has voiced reservations about the new law: civil rights advocates. Civil rights leaders have praised the law as an improvement over the No Child Left Behind Act, which tied federal funding with school performance. But they have voiced concerns that ESSA, which largely leaves accountability goals up to the states, could leave marginalized students even further behind.

Their big fear is that under the new law, states may not hold schools truly accountable for poor performance, making it harder to close the “achievement gap” for disadvantaged students. Despite all of the No Child Left Behind Act’s flaws, education researchers found that it led to small but substantial gains in student achievement, particularly for black, Hispanic, and low-income students.

The new law has placed two key progressive constituencies—unions and civil rights groups—at odds. Unions are celebrating the return of power to states and local districts, and an end to continuous testing mandates. But a broad coalition of civil rights groups that includes the Southern Poverty Law Center and the NAACP, has cautioned that the Every Student Succeeds Act must not let states off the hook for failing to educate the nation’s most vulnerable students.

Civil rights have long been at the heart of American federal education policy. ESSA reauthorizes the Elementary and Secondary Education Act, a civil rights law originally passed in 1965 that was designed to raise the academic achievement of marginalized student groups, including the poor, the disabled, racial and ethnic minorities, and non-native English speakers.

It took years for Congress to pass the Every Student Succeeds Act, and throughout the process civil rights groups worked hard to ensure that their concerns were being heard. While ESSA expands on important reporting requirements first imposed by No Child Left Behind, the new law does not require states to respond to inequities if data reveal that they exist.

“Data is always an important first step, but what we wanted was a requirement that when there are disparities, the schools, districts, and states have to take action,” explains Liz King, the director of education policy at the Leadership Conference on Civil and Human Rights. (The law also does not require states to disaggregate Asian American and Pacific Islander data by ethnicity, which civil rights advocates worry will obscure important differences.)

Most importantly, civil rights organizers voice serious concerns that states will now essentially hold themselves accountable. Under No Child Left Behind it was the federal government, not the states, that had the last word on school performance.

“The hard-learned lesson of the civil rights community over decades has shown that a strong federal role is crucial to protecting the interests of underserved students,” wrote the Leadership Conference on Civil and Human Rights in a letter to Capitol Hill last year. While the law includes some measures that will help advocates push states and districts to ensure that disadvantaged students don’t slip through the cracks, some experts say it will be harder for the federal government to intervene in the event that states fail to act.

One specific equity measure that civil rights groups tried and failed to win during ESSA negotiations was the closing of the so-called “comparability loophole.” In order for states to access Title I funds, which are federal dollars that go to high-poverty districts, they have to demonstrate that they’re providing “comparable” levels of services to both Title I schools and more affluent schools. The new law, like the old law, allows states and districts to exclude real teacher salary costs from expenditure calculations. That means that a district could be considered “comparable” if it has a bunch of novice, inexpensive teachers in one school, and many highly paid veteran teachers in another.

According to a 2015 report issued by the Center for American Progress, a liberal think tank, 4.5 million students attend inequitably funded Title I schools—receiving about $1,200 less per student on average than wealthier schools in their districts. (Closing the loophole would only address intra-district disparities, but advocates say that it’s an important step for educational equity nonetheless.)

Historically, teachers unions have been wary of efforts to close the loophole, fearing that districts might respond by making veteran teachers transfer involuntarily to more disadvantaged schools. In recent years, however, unions have softened their stance, recognizing that districts could respond to inequities not through forced transfers, but by investing in disadvantaged schools in other ways. Still, the National Education Association and the American Federation of Teachers did not push as hard to close the loophole during ESSA negotiations as civil rights groups did.

Nevertheless, civil rights groups did win some of their key demands.

Although Congress did not close the “comparability loophole,” districts will now be required to report actual expenditure data at the school level, something civil rights leaders say is a huge improvement over No Child Left Behind. (Other data reporting requirements have also been expanded.) Civil rights advocates hope that this new level of transparency will go a long way towards highlighting funding inequities, and pave the way for further reforms.

States will now also have to do more to help students become proficient in English, and there are more accountability measures in place to ensure schools are making progress toward that goal.

“This was a very important goal for us; research suggests the longer you’re identified as an English-language learner, the less likely you are to graduate high school,” says Brenda Calderon, ‎the Education Policy Analyst at National Council of La Raza, a Latino advocacy organization.

In addition, no more than 1 percent of students with disabilities may now be given so-called alternative assessments, a form of test less rigorous than what the general student population takes. This was a key priority for disability rights advocates, who said too many students with special needs were being separated from their peers without good reason. Taking alternative assessments can have negative consequences, like preventing disabled students from graduating with a regular high school diploma.

The law also offers some additional protections for homeless children and children in foster care, expands opportunities for children in the juvenile justice system, and includes measures to help schools deal with emotional trauma.

The big challenge for civil rights groups during negotiations was that Republicans control both the House and Senate. For years, conservatives have been seeking to reduce the federal government’s role in education policy, and to a large extent, they succeeded. It didn’t help the civil rights coalition that teacher unions largely agreed with the GOP on the need to shift power back to the states.

Over the next two years, legislators and advocates on the state and federal levels will work through a regulatory process to flesh out what the requirements of the new education law actually mean.

“What we're hoping for is some real state and federal leadership, because it doesn't serve anyone well if we wait until things aren't working,” says King, of the Leadership Conference on Civil and Human Rights. “We want to make sure there are affirmative steps to ensure there is equity. We’re planning to help influence the regulatory process, to shape what the terms in the law actually mean, and to inform guidance about how to comply with the law.”

Civil rights groups are bracing for what they say will be a lot of challenging fights in all 50 states. The Every Student Succeeds Act will require parents and advocates to continually pressure states and districts to make sure disadvantaged students get the same education as their more-privileged peers. It’s an uphill battle, civil rights advocates acknowledge.

Yet along with conservatives and teachers unions, civil rights organizers have praised the new law’s expanded data reporting requirements, the continuation of annual student testing in third through eighth grades, and the reduction of harsh, test-linked penalties. Everyone, for now at least, agrees that the new law is an improvement over No Child Left Behind.